Question

Draw the Lewis formula of benzene, \(\mathrm{C}_{6} \mathrm{H}_{6}\), a cyclic compound.

Short answer

The Lewis structure of benzene consists of a hexagonal ring of six Carbon atoms, each attached to one Hydrogen atom. Within the ring are alternating single and double bonds between the Carbon atoms. This satisfies the octet rule for each Carbon and hydrogen and accounts for all valence electrons.

Step-by-step solution

Determining Total Valence Electrons

Firstly, calculate the total number of valence electrons in a benzene molecule. Each carbon atom (C) has 4 valence electrons, and each hydrogen atom (H) has 1. So, for benzene (C6H6), total valence electrons = 6*(4) + 6*(1) = 30.

Drawing Basic Structure

Draw a simple structure by placing six Carbon atoms (C) in a hexagonal ring and attaching one Hydrogen atom (H) to each Carbon. Don't draw any bonds yet.

Adding Single Bonds

Add single bonds between each Carbon atom and the Hydrogen attached to it, and between each pair of Carbon atoms. This completes 24 out of the 30 valence electrons (each bond represents two electrons).

Completing Octet for Each Carbon Atom

Each Carbon atom currently has 3 bonds (hence, 6 electrons). It needs 2 more electrons to complete its octet. But here, only 6 electrons (30 initial - 24 used) remain. Hence instead of two single bonds, one double bond is drawn between each alternate pair of Carbons. This results in an alternating single-double bond structure around the ring, satisfying the octet rule and accounting for all valence electrons.

Key concepts

Valence Electrons

Valence electrons are crucial in understanding molecular structures. They are the outermost electrons of an atom and are responsible for chemical bonding. In the case of benzene (\(\mathrm{C}_{6}\mathrm{H}_{6}\)), we calculate valence electrons by considering each atom's contribution. Carbon contributes four valence electrons, while hydrogen contributes one. By summing these, we get the total valence electrons available for bonding in benzene.For benzene:

• Carbon: 6 atoms with 4 electrons each = 24 electrons
• Hydrogen: 6 atoms with 1 electron each = 6 electrons
• Total valence electrons = 30

These electrons define how atoms in benzene bond with each other. Understanding this concept allows us to predict how electrons are shared among atoms and how molecules achieve stability. Valence electrons, therefore, play a pivotal role in determining the structure and reactivity of a compound.

Octet Rule

The octet rule is a chemical principle that describes how atoms bond together to reach a stable configuration. Most atoms aim to have eight electrons in their outermost shell, similar to the electron configuration of noble gases. This rule helps explain the behavior of atoms in molecules like benzene. In benzene:

• Each carbon atom initially bonds with one hydrogen and two carbon atoms, forming three bonds (6 electrons).
• The goal is for each carbon to have a total of eight electrons in its valence shell.
• By creating alternating double bonds, each carbon attains the necessary eight electrons.

The octet rule emphasizes the tendency of atoms to stabilize by sharing electrons, leading to the formation of double or single bonds as needed. It's particularly useful for drawing Lewis structures, as it guides how many electrons are shared or paired between atoms.

Chemical Bonding

Chemical bonding is the process that holds together atoms in a molecule. Bonds form when atoms share or transfer valence electrons to achieve stability. There are different types of chemical bonds, but in benzene, covalent bonding is predominant. In benzene's structure:

• Single bonds are formed between carbon and hydrogen atoms, sharing one pair of electrons.
• Carbon atoms form alternating single and double bonds within the ring, sharing electrons to satisfy the octet rule.

This arrangement creates a stable, resonating structure where electron density is evenly distributed across the molecule. Covalent bonds in benzene are strong and durable, and they provide insights into the sharing of electrons that maintain the molecule’s integrity. Understanding these bonds helps comprehend the chemical properties and reactivity of benzene and other organic compounds.